Ofcom has opened an investigation into the “cash for access” sting by Channel 4’s Dispatches programme – despite not having received a single complaint.

Channel 4 had asked the regulator to investigate its February 23rd programme, which reported allegations concerning former foreign secretaries Sir Malcolm Rifkind and Jack Straw.

Both were cleared last week by the parliamentary commissioner for standards, which said that Dispatches and the Daily Telegraph – who had teamed up for the investigation – had not accurately reported the exchanges they had covertly filmed.

And in a highly unusual move, the regulator has now said it will investigate whether any rules had been broken.

An Ofcom spokesperson said: “Ofcom is investigating whether Channel 4’s Dispatches programme broke rules requiring fairness in programmes. Once we have concluded our investigation into the broadcast we will publish our decision.”

In a statement earlier this month, Daniel Pearl, Channel 4’s deputy head of news and current affairs, said: “This programme raised important questions which concern voters about how senior politicians are able to use their public office for personal financial gain. This is a matter of public interest and was a legitimate journalistic investigation.

“We’re confident in our journalism and have decided to take the unprecedented step of inviting our statutory regulator Ofcom to investigate the report.”